Solo Hawaiian slack guitar, calm and tranquil, very soothing and heartening. Slack guitar became popular in the 1960s and again in the 1970s during the Hawaiian Cultural Renaissance, but is thought to have developed in the 1800s in Hawaii. Keywords: Slack Guitar Means to Begin With a Classically Tuned Steel Guitar, Then the Player 'De-Tunes' Or Slightenly Loosens the Strings. Heartwarming, Beautiful